Signal-translating system



Feb. 28, 1939. N. P. CASE SIGNAL TRANSLATSING SYSTEM Filed Oct. 14, 1936 INVETOR. NELSON P. A E

ATTORNEY,

. 50 serve to maintain the signal output volume level vacuum tube connected so that the elective rei Patented eb. 28, 1939' UNITED STATES PATENT oFFicE 2,148,604 SIGNAL-TRANSLATING SYSTEM Nelson P. Case, Great Neck, N. Y., assigner to Hazeltine Corporation, a. corporation of Delaware Application October 14, 1936, Serial No. 105,464 9 claims. k(o1. 25o-20) 'I'his invention relates to signal-translating sysdo not serve to hold the signal at the input circuit tems, and ,more particularly to adjustable couof the rst amplier at the optimum amplitude.

, pling arrangements for use in such systems. Certain mechanical arrangements have also been In its broader aspects, the invention is directed devised heretofore for providing automatic gain y to coupling systems `generally and to provision control of antenna coupling systems. Such ar- 5 of means for adjusting the coupling provided rangements, however, have proved unsatisfacthereby for any desired purpose.k The invention tory in that the control provided thereby was not is specifically concerned withantenna coupling sufliciently rapid, or was otherwise unstable or systems and with the provision of means, rapid undependable.

1o and dependable in operation, for automatically In general, it is an object of the invention to 10 controllingthe gain of such systems in accordprovide an improved coupling system embodyance with the amplitude of signals passed thereby. ing means for adjusting the coupling provided In a high-frequency signal-receiving system, in thereby, which is adapted for use in any desired order to obtain satisfactory reproduction of relan system to provide any desired change in the chartively weak received signals, such as signals from acteristics of the system which may be produced l5 ydistant stations, it is highly desirable that the by a coupling adjustment. antenna circuit be coupled to the iirst vacuum More particularly, it is an object of the intube amplifier of the signaling system by a vention to provide an improved adjustable ancoupling'system which provides a high gain, so tenna coupling system embodying one or more `that a maximum signal-to-noise ratio may be `of the characteristics described above. 20 obtained at the input circuit of the first ampli- It is a further object of the invention to proer. Asis well known, however, if such asystem vide an improved antenna coupling system of is adjusted toproduce a high gain when relathe character described embodying means, rapid tively strong signals, such as signalsfrom nearby and dependable in operation, for automatically stations, are received, such signals will be imcontrolling the gain of the system in accordance 25 pressed upon the input circuit of the rst amplier with the amplitude of the signal passed thereby. at such high amplitudes as` to eect overloading of In accordance with the present invention, there vthe amplier, which causes distortion, whistles, is pro-vided, in a signal-translating system, a and cross modulation between desired and un- Coupling System WhiCh includes input and Out* desired signals. YIt is desirable, therefore, that put Circuits and an arrangement OI adjusting 3o the gain of the antenna coupling system be high the COUDliHg- This arrangement preferably 00mn for the reception of relativelyweak signals and prises a vacuum tube connected to simulate an Vreduced forV the reception of relatively strong adjustable reactance element, for example, being signals, so that the amplitudes of the signal inso connected that the effective reactance of its put to the firs-t amplifier will be maintained at input circuit provides a coupling reactance which 35 approximately optimum value for received signals is adjustable by changing the transconductance of all amplitudes.y of the tube. In certain embodiments of the Moreover, due to the well-known phenomenon invention, means are 4provided for eecting the of. fading, the amplitude of any particular signal adjustment of the coupling reactance means 40 being received may vary over an extremely wide automatically and inversely in accordance with 40 range, that is, from avery low to a relatively high the amplitude of signals passed by the system, value, at times with great rapidity. `Compensathereby to control the gain of the coupling systion for this condition by adjustment of the antem and maintain the amplitude of the signal tenna gain, therefore, requires an extremely rapid output ktherefrom Within a relatively narrow control which is dependent upon, and immedirange fora wide range of signal input amplitudes. 45 ately responsive to, the amplitudes ofthe signal A preferredk embodiment of the invention combeing received. prises an antenna coupling system for coupling While various systems of automatic amplicaan antenna circuit to a resonant signal-translattion control or A. V. C. have been devised, which ing circuit. The gain control means includes a of systems to Whichrthey are applied within a actance of its input circuit provides an adjust- 0 relatively narrow range, or substantially constant, able coupling capacitance serially included in for a wide range of received signal intensities, theantenna circuit. Means are provided for such arrangements operate to control the vacderiving a bias voltage proportional to the amplinum-tube amplifiers of the system and, hence, tude of signals passed by the system and for 55 applying this voltage negatively to a control grid of the tube to adjust the transconductance of the tube, thereby to control the effective reactance of its input circuit and, hence, the gain of the system automatically and directly in accordance with the signal amplitudes. Other embodiments of the invention may be employed to provide coupling systems wherein the coupling is automatically adjusted for various other purposes, as will be hereinafter more fully explained.

For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the accompanying drawing, Fig. 1 is a circuit diagram, partly schematic, of a complete superheterodyne radio receiver including an antenna coupling system embodying the invention; and Fig. 2 is a circuit diagram similar to Fig. l, but including a modified form of the coupling system of the invention, providing an interstage coupling in the receiver.

Referring now more particularly to Fig. 1 of the drawing, there is shown a radio receiver including a coupling system, indicated generally at IIJ, `interconnecting an antenna circuit comprising an antenna II and ground Ila, and the input circuit of a radio-frequency amplifier tube I2. Connected in cascade with the radio-frequency amplifier tube I2, in the ordernamed, are an oscillator-modulator I3, an intermediate-frequency amplifier I4, a detector and automatic amplification control or A. V. C. supply I5, an audio-frequency amplifier I6, and a sound reproducer or loud-speaker I'I. The coupling system I0 is shown in detail and it, together with the parts of the system associated therewith which embody the present invention, will be hereinafter further described. It will be understood that the several parts which are illustrated in the drawing schematically may be conventional in their construction and operation, the details of which are well understood in the art rendering description thereof unnecessary herein.

Neglecting for the moment the particular construction and operation of the parts of the system embodying the present invention, the system described above includes all of the features of a conventional superheterodyne receiver. The operation of such a receiver being well understood in the art, detailed explanation thereof is deemed unnecessary. In brief, however, a desired modulated-carrier signal intercepted by the antenna is selected and amplified by the antenna coupling system I and amplier tube I2, and converted by the oscillator-modulator to an intermediatefrequency signal. This signal is selected and amplied by the intermediate-frequency amplifier I4 and translated therefrom to the detector I5, wherein theaudio frequencies of modulation are derived. The audio frequencies: of modulation are amplified in the audio-frequency amplifier I6 and reproduced in the loud-speaker II in conventional manner. Biasing potentials developed by the A, V. C. supply I are supplied, by way of suitable leads indicated at I5a, to control the gain of one or more of the tubes of the intermediate-frequency amplifier and oscillator-modulator, to maintain the amplitude of the signal output of the amplifier I4 within a relatively narrow range for a wide range of received signal amplitudes.

Referring now more particularly to the portion of the system embodying the present invention, the coupling system I0 includes a resonant signaltranslating circuit I8, the arms of which comprise, respectively, an inductance I9 and a coupling condenser 20 connected in series with a tuning condenser 2l. In order to control the gain ofthe system, the antenna II is connected to ground IIa by way of a blocking condenser 23, the input circuit of a vacuum tube 22, and the condenser 20. The condenser 20 is thus a coupling condenser common to both the antenna circuit and the signal-translating circuit I8; the tube -22 is preferably a pentode, as illustrated, al-

though any vacuum tube having three or more electrodes arranged to provide a substantial value oi effective input circuit capacitance may be employed. A condenser 24 is connected between the control grid and anode to increase the effective grid-to-cathode capacitance and a high impedance, for example, a resistor 25, is included in the anode circuit of the tube.

Operating voltages are supplied to the anode of the tube b'y way of the resistor 25 and to the screen from suitable sources, as indicated atV +B and -i-SC, respectively. The cathode of the tube 22 is preferably maintained at the same average potential as be connected thereto by way of a radio-frequency choke coil 26, a suitable biasing resistor 2l and by-pass condenser 21a being included in the common cathode circuit of the tubes I2 and 22.

As is well understood, the interelectrode ca.- pacitances of a vacuum tube include those of the cathode-to-grid, grid-to-plate, and grid-to-plate and cathode connected together. With a high impedance in the anode circuit of the tube, such as the resistor 25, the eifective grid-to-cathode capacitance is approximately that represented by the formula:

C=CGc-I-(,LL-I1)CGA where:

C=the effective grid-to-cathode capacitance. Y

CGc=the geometrical grid-to-cathode capacitance.

Cc`A=the grid-to-anode capacitance.

fi:the grid-to-plate voltage amplification of the tube and circuit.

The effective grid-to-cathode capacitance, therefore, varies with any factors which affect the transconductance of the tube. Such factors include, for example, the anode circuit load impedance, the screen and anode voltages, and the grid-bias voltage. This effective capacitance is, therefore, admirably adapted for providing an adjustable coupling capacitance in a coupling system, and in accordance with the present invention it is so utilized.

In order to vary the transconductance of the tube 22 and, hence, the effective grid-to-cathode capacitance of the tube, in the present instance a control-bias voltage is applied to its control grid. For the purpose of developing this voltage, a broad band intermediate-frequency amplifier 28 and an automatic amplification control or A. V. C. rectifier 29 are connected in cascade, in the order named, to the output circuit of the oscillator-modulator designed to pass a band of frequencies which is substantially as wide as that passed by the coupling system Ill; that is, it passes and ampliiies not only the desired signal to which the system is tuned, but also undesired-signals which are passed by the antenna coupling system and which may the cathode of the tube I2 and may I3. The amplifier 28 is Y necessary. The A. V. C. rectier Lat kcontrol grid returns ofthe tubes have Vsuficient amplitude to be capablev of overloading the amplier I2, causing distortion, cross modulation, or interference. The construction of an ramplifier having the desired broad bandpass characteristic is well understood in the art and4 adetailed description thereof is deemed un- Y y e is designed and operates in a conventional manner to develop a bias voltage proportional to the carrier amplitude of the signals supplied thereto, and this bias `rvoltage is applied negatively by Way of a suitable resistor 23a` to the control grid of the tube22.

This bias voltage is also applied to the control grid of the amplifier tube I2 to'provide a supplemental amplification control. y

l In lorder to provide a manual gain control of the antenna couplingsystem and radio-frequency amplifier, a switchV 30 may be included in the control-bias voltage lead, by means of which the 22 and I2 may be disconnected from the output circuit of the rectifier 29 and connected to an adjustable tap 3m on avoltage divider resistor 3I, connected to a suitable 'source of biasing potential, such as a battery 32.` i Y For the usual automatic operation of the system-,fthe switch 3!) is positioned, as illustrated.

The operating potentials applied to the tube 22 l including the initial fixed grid-bias voltage supplied rby resistor 21, the Value of thecondenser 24,

vand the constants of the other circuit elements associated with the tube 22 are adjusted, so that, in the absence of a signal or for relatively weak signals, theeffective grid-to-cathode capacitance of the tube is a maximum, giving the maximum gain for the coupling system. A satisfactory maximum value of effective capacitance has been vfound to' be one which is between one and ten times the value of the antenna capacitance. Hence, when relatively Weak 'signals are received, the gain'of the couplingy system is high, and a relatively strong signal and a high signal-tonoise ratio are. obtained at the input circuit of the tube I2. l

When, however, there are received signals, including reither the desired signal to which the system isA tuned or undesired signals on carriers adjacentv the desired signal carrier, which would be of sufficiently great amplitude at the input circuit of the tube l2 to 'overload this tube if maximum gain were maintained for the antenna coupling system, these signals are amplified by the amplifier 28 and rectified by the rectifier 29. The unidirectional voltage derived therefrom is applied negatively to the control grids yof the tube 22 and I2. The transconductance of the tube y22 and, hence, its effective grid-to-cathode capacitancearethus varied inversely in accordance withy the received signal amplitudes; that is', the ycapacitance in series in the antenna circuit is reduced, preferably to an amount substantially less than the antenna capacitance.

Thegain of the antenna coupling system is thereby automatically controlled inversely in accordance withthe ampliture of the signals passed thereby. iBy this arrangement, therefore, the Igainy of the antenna coupling system is so controlled as to provide automatically the maximum gain permissible'for all received signals of a Wide range of amplitudes ywithout overloading i the radio-frequency amplifier tube I2.. A supplemental amplification control is effected in the tube'IZ by the application of the negative biasy voltage to the grid of the tube, variabledirectly .condenser 49.

in accordance with the received signal amplitudes.

In Fig. 2 there is illustrated a superheterodyne receiver which embodies the present invention in a modified form. The system of Fig. 2 is, in general, sirnilar to the receiver of Fig. 1, and like parts are indicated by the same reference numerals in the two figures. The description of the general construction and operation of the receiver of Fig. 1, set forth above, is equally applicable to the receiver of Fig. 2 and, therefore, need not be repeated While an automatically controlled antenna coupling system, such as is shown in Fig. 1, may be embodied in the receiver of Fig. Y2 if desired, for the sake of brevity this has not been illustrated.

In Fig. 2 an improved coupling system according tothe present invention is indicated generally at 33. This system is utilized as an interstage coupling between the oscillator-modulator I3 and the intermediate-frequency amplifier I4. The output circuit of the oscillator-modulator I3 includes an inductance 34 tuned to the intermediate-frequency carrier by a condenser 35, and the input circuit of the intermediate-frequency amplifier I4 includes an inductance 36 tuned to the intermediate-frequency by a condenser 31. The two tuned circuits 34, 35 and 3B, 31 are electromagnetically isolated from each other by suitable shields indicated at 38. The lower terminals of the condensers 35 and 31 are connected directly to ground, while the lower terminals of the inductances 34 and 36 are grounded by way of direct current blocking condensers 4I] and 4I, respectively, and common coupling condenser 33. Operating potential is supplied to the oscillatormodulator from a suitable source, indicated as -l-B, by way of an isolating resistor 42 and the inductance 34.

'A vacuum tube 44, similar in its connections and operation to the tube 22 of Fig. 1, is provided for the coupling system 33. A condenser 45 is connected between the control grid and anode of the tube 44, and its input circuit is connected effectively in parallel with the coupling condenser 39. Operating potentials are applied to its anode,`by way of a resistor 46, to its screen, and to its cathode, from suitable sources, as indicated at +B, -l-Sc, and -i-C, respectively. The effective capacitance of the input circuit of the tube 44 is thus included in parallel with the condenser 39 and se-rves as an adjustment on the coupling capacitance between the circuits 34, 35 and 36, 31. In 'this embodiment, the unidirectional control-bias voltage is developed by the A. -V. C. supply I5 across a resistor 41, which is grounded at an intermediate point. A portion of this voltage is applied positively to the control grid of the tube 44 by way of suitable isolation resistors 48, the junction of which is by-passed to ground by The constants of the circuit elements associated with the tube 44, including the initial voltages applied thereto, are so proportioned as to bias the tube beyond cutoff in the absence of a signal of `sufficient strength to effect veloped across the resistor il and applied positively to the control grid of the tube d4, the effective capacitance of the input circuit of the tube is increased and the coupling between the two circuits 3e, 35 and Sii, 3l is, therefore, decreased. Such decrease in coupling reduces the gain of the system and, by virtue of this eiect, the amplitude of the signal output from the coupling system is maintained within a relatively narrow range for a wide range of signal amplitudes.

Supplementing the gain control provided by the coupling adjustment, the unidirectional bias voltage developed across the resistor 4l may be applied negatively to the control grids of one or more of the amplifier tubes of the system in accordance with conventional A. V. C. practice. For example, this voltage may be applied as shown by way of an isolating resistor 5l and the inductance 36 to the control grid of the first tube of the intermediate-frequency amplifier ld.

From the above description it will be apparent that the present invention provides a novel, practical, and eiiicient arrangement whereby the coupling between a pair of circuits may be readily adjusted for various desired purposes, and more particularly it provides a highly satisfactory arrangement whereby the gain of an antenna coupling system may be controlled to obtain the optimum value for all received signal conditions.

While there have been described what are at present considered to be the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modiiications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a signal-translating system, a coupling system comprising an input circuit, an output circuit, means or coupling said circuits, and means for controlling the coefficient of coupling between said input and output circuits comprising a vacuum tube having electrodes connected with said circuits and means coupling said electrodes whereby said tube simulates a reactance element connected in circuit with said circuits for modifying the coefficient of coupling therebetween and adjustable with the transconductance oi said tube and means for adjusting said transconductance of said tube.

2. In a signal-translating system, a coupling system comprising an input circuit, an output circuit, means for coupling said circuits, a vacuum tube having electrodes connected with said circuits and means coupling said electrodes whereby the input circuit of said tube provides an effective reactance connected in circuit with said input and output circuits for modifying the coeiilcient oi coupling therebetween and adjustable with the transconductance of said tube, and means for controlling the gain oi said coupling system thereby to maintain the amplitude of the signal output therefrom within a relatively narrow range for a wide range of signal input amplitudes comprising means for adjusting the transconductance of said tube in accordance with the amplitude of signals passed by said system.

3. In a signal-translating system, a coupling system comprising an input circuit, an output circuit, means for coupling said circuits, a vacuum tube having anode, cathode, and grid electrodes, means for applying operating potentials to said electrodes, said tube having a high impedance included in its anode circuit and a substantial reactive coupling between its grid and anode, whereby its input circuit provides an effective reactance adjustable with the transconductance oi said tube, and means for controlling the coefficient of coupling between said input and output circuits of said coupling system including the input circuit of said tube and means for adjusting the transconductance of said tube.

4. In a signal-translating system, a coupling system comprising an input circuit, an output circuit, means for coupling said circuits, a vacuum tube having anode, cathode, and control grid electrodes, means for applying operating potentials to said electrodes, said tube having a high impedance included in its anode circuit and a substantial reactive coupling between its grid and anode, whereby its input circuit provides an effective reactance adjustable with the transconductance of said tube, means for controlling the coefcient of coupling between said input and output circuits of said coupling system for varying the gain of said system including the input circuit of said tube, and means for applying a controllable bias voltage to said control grid.

5. In a signal-translating system, an antenna coupling system comprising an antenna circuit, a resonant signal-translating circuit, means for coupling said circuits, and means for controlling the gain of said coupling system comprising a vacuum tube having electrodes connected with said antenna circuit and means coupling said electrodes whereby the input circuit of said tube provides an effective coupling reactance included in said antenna circuit and adjustable with the transconductance of said tube and means for adjusting said transconductance to vary said coupling provided by said effective reactance.

6. In a signal-translating system, an antenna coupling system comprising an antenna circuit, a resonant signal-translating circuit, means for coupling said circuits, a vacuum tube having anode, cathode, and control grid electrodes, means for applying operating potentials to said electrodes, said tube having a high impedance in its anode circuit, and a substantial reactive coupling between its grid and anode, whereby its input circuit provides an effective reactance adjustable with the transconductance of said tube, and means including the input circuit of said tube for controlling the coupling between said antenna and signal-translating circuits and means for adjusting the transconductance of said tube.

7. In a signal-translating system, an antenna coupling system comprising an antenna circuit, a resonant signal-translating circuit, means for coupling said circuits, a vacuum tube having anode, cathode, and control grid electrodes, means for applying operating potentials to said electrodes, said tube having a high impedance in its anode circuit and a substantial reactive coupling between its grid and anode, whereby its input circuit provides an eiiective reactance adjustable with the transconductance of Vsaid tube, and means for controlling the gain of the system including the input circuit of said tube controlling the coupling between said antenna and signal-translating circuits and means for applying a controllable bias voltage to said control grid.

8. In a signal-translating system, an antenna coupling system comprising an antenna circuit, a resonant signal-translating circuit, means for coupling said circuits, a Vacuum tube having anode, cathode, and control grid electrodes, means for supplying operating potentials to said electrodes, said tube having a high impedance in v its anode circuit and a substantial reactive coupling between its grid and anode, whereby its input circuit provides an effective reactance adjustable with the transconductance of said tube,

` means including the input circuit of Said tube for system within a' relatively narrow range for a wide range of received signal amplitudes comprising means for applying said Voltage to said control grid.

9. In a signal-translating system, an antenna coupling system including an antenna circuit and a resonant signal-translating circuit, a vacuum tubey amplifier having a grid electrode, coupled to said signal-translating circuit, a second vacuum tube having anode, cathode, and control grid electrodes, means for applying operating potentials to the electrodes of said tubes, said second vacuum tube having a high impedance in its anode circuit and having a substantial reactive coupling between its grid and anode, whereby its input circuit provides an eiective reactance adjustable with the transconductance of said second tube, the input circuit of said second tube being included in said antenna circuit, a conductive connection between the grids of said tubes, means for vdeveloping a control bias voltage, and a connection from the last said means to said conductive connection, whereby said bias voltage is simultaneously applied negatively to the control grids of both said tubes to control the gain of the system.

NELSON P. CASE. 

